Just like any other subject in math, Geometry is
loaded with a wide variety of subtopics - including
the ubiquitous Trigonometry. Just as the previous
pages however, we will focus on the basics - again
to help stir the memory a bit.

The basic form of
Geometry - that is lines, perimeters, areas - is
called Euclidean Geometry named after its Greek
inventor, Euclid. Another name for Euclidean
Geometry is Plane Geometry.

Two angles are complimentary when the
sum of their angles is 90o. In
the image on the left, angles A and B are
complimentary and angles A and C are also
complimentary.

The remaining angle
definitions will use the image above.

Supplementary Angles:

Two angles are supplementary is the sum of the
angles is 180o. Angles 1 and 2 as well as
angles 2 and 4 are supplementary angles.

Opposite (Vertical) Angles:

The intersection of two lines (m1 and m3) form 4
angles. Opposite angles are equal (congruent).
Angles 1 and 4 as well as angles 2 and 3 are
congruent.

Alternate Angles:

Lines m1 and m2 are parallel. Angles 4 and 5 are
alternate interior angles and are congruent. Angles
3 and 6 are also interior angles but are not
congruent. Angles 2 and 7 are alternate exterior
angles and are congruent. Angles 1 and 8 are also
alternate exterior angles but are not congruent.

Triangles:

The three angles of a triangle always total 180o.
An equilateral triangle is a triangle with 3 equal
sides and all 3 angles are 60o.

An isosceles triangle is a triangle with
two equal angles. The two equal angles must
each be less than 60o. The image
on the left illustrates angles A and B are
equal.

The height of a triangle is defined by the base.
Once any side of a triangle is chosen, the angle
between the base and height can change, but the but
measure of the height remains the same.